Microwave heating apparatus for rotatable articles

ABSTRACT

An applicator is provided in combination with a microwave nonradiant energy source having means for automatically sensing and maintaining a predetermined distance with respect to the article being heated. In one embodiment a tire having a nonuniform cross-sectional contour is continuously rotated and axially displaced while the sensor means contact the outer surfaces of the tread to track the disposition of the tire relative to an energy applicator such as a horn radiator mounted on a motorized cart. Electromechanical actuators and limiters are incorporated with the sensor means to generate electrical data to control the movement of the energy radiator in a forward and backward direction. Another embodiment comprises a motorized cart arrangement with a sloped track bearing the sensor and energy radiator means utilizing the force of gravity to maintain contact.

United States Patent n91 Peterson [4 1 Feb. 18,1975

1 1 MICROWAVE HEATING APPARATUS FOR ROTATABLE ARTICLES [75] Inventor: Robert A. Peterson, Canton, Mass.

[73] Assignee: Raytheon Company, Lexington,

Mass.

[22] Filed: Oct. 15, 1973 [21] Appl. No.: 406,770

[52] US. Cl. 219/1055, 219/1055 [51] Int. Cl. H05b 9/06 [58] Field of Search 219/1055, 125, 10.55 R,

[56] References Cited UNITED STATES PATENTS 2,839,663 6/1958 Mccollum 219/125 R 3,745,291 7/1973 Peterson 219/1055 3,835,282 9/1974 Sass 219/1079 m r XGWMH-TBIBEKA. Reynolds Attorney, Agent, or Firm-Edgar O. Rost; H. A. Murphy; Joseph D. Pannone [5 7] ABSTRACT An applicator is provided in combination with a microwave nonradiant energy source having means for automatically sensing and maintaining a predetermined distance with respect to the article being heated. in one embodiment a tire having a nonuniform cross-sectional contour is continuously rotated and axially displaced while the sensor means contact the outer surfaces of the tread to track the disposition of the tire relative to an energy applicator such as a horn radiator mounted on a motorized cart. Electromechanical actuators and limiters are incorporated with the sensor means to generate electrical data to control the movement of the energy radiator in a forward and backward direction. Another embodiment comprises a motorized cart arrangement with a sloped track bearing the sensor and energy radiator means utilizing the force of gravity to maintain contact.

2 Claims, 3 Drawing Figures A r V VA I 50 V g 54 38 SENSING AND CONTROL 34 Z aura. M EANS ENERGY APPLICATOR -i1 llllllllllllllllllllllli 26 P 54 40 -|um I] ELECTRICAL 2a SUPPLIES 50 g CONTROESN D 52 MICROWAVE HEATING APPARATUS FOR ROTATABLE ARTICLES BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to microwave heating apparatus and means for sensing and positioning an energy applicator a predetermined distance from an article during processing.

2. Description of the Prior Art Poor thermal conductors, such as rubber goods, particularly pneumatic type tires require lengthy heating times with radiant energy sources to reach the working temperatures for vulcanizing, molding or recapping. Such products include both natural as well as synthetic rubber materials along with other ingredients of a carbonaceous nature which are ideal for absorption of nonradiant electromagnetic energy. Microwave heating apparatus is now widely utilized in the processing of such materials as rubber, foods, paper, wood, leather, plastic and other poor thermal conductors. High frequency energy absorbed by such materials creates high frequency oscillations of the molecules within the article to cause elevated temperatures due to molecular friction. The high frequency energy is generated by such sources as the magnetron which is now wellknown in the art and is described in the text Microwave Magnetrons, Vol. 6, Radiation Laboratory Series, by G. B. Collins, McGraw-Hill Book Company, Inc., New York 1948. The operating frequency is allocated by the Federal Communications Commission and, typically, the industrial, scientific, and medical bands are utilized having frequencies of 915 il3 MHz and 2450 i 50 MHz. For the purposes of the present description the term Microwave is defined as nonradiant energy in the portion of the electromagnetic energy spectrum having wavelengths in the order of 1 meter to l millimeter and frequencies in the order of 300 MHz to 300 GHz.

Examples of prior art energy applicators used in microwave heating apparatus for the preheating of rubber tires is found in U.S. Pat. No. 3,566,066, issued Feb. 23, 1971, to J. Borthwick et al. where the tires are carried on a rotatable support within a chamber having a fixed cross-sectional dimension with the energy being distributed by means of a vane-type mode stirrer adjacent to a waveguide feed. it is difficult with such apparatus to obtain substantially uniform heating throughout the product, particularly in the case of pneumatic type tires where a thicker cross section is found in the shoulder region of the tire treads relative to the center. Another example of the prior art is shown in U.S. Pat. No. 3,745,291, issued July l0, 1973 to R. A. Peterson et al. and assigned to the assignee of the present invention. This apparatus provides for processing of pneumatic type tires with an applicator including at least one horn-type radiator heating predetermined areas of the tire casing. The ends of the horn-type radiator facing the article being heated are contoured to conform to the article being processed and the path of travel. The support for the article being heated is positioned within the enclosure and is capable of axial as well as rotating motion by suitable gearing means to provide for the uniform application of the energy across the entire surface ofthe article with the energy being radiated from a fixed applicator. Since tires have a substantially nonuniform cross-sectional area with the thicker region in the shoulder portions, varying heating times are required to substantially equalize the overall temperature of the article prior to vulcanizing or recapping. To heat such articles with microwave energy it is necessary to continuously rotate and axially move the article with the rate of movement being programmed to obtain a predetermined temperature profile across-the entire article. As a result of this processing the areas of thicker dimension receive a higher heat concentration while lower heat is provided for the thinner areas of the tread. in the processing of the rubber tires. particularly those having diameters as large as 15 feet, the heating apparatus enclosure is provided with movable walls having the energy applicators mounted thereon, and such applicators may be provided in four quadrants of a circular path to provide for more uniform heating. The energy applicators may also be staggered to provide such uniform heating. in this apparatus the uniform heating is attained by providing a variable rate of movement relative to the fixed horn-type contoured radiators to compensate for the change in the crosssectional dimension of the article.

Other, less costly, ways of achieving a uniform heating of a nonuniform cross-sectional article is desirable, particularly in view of the fact that large diameter tires cost many thousands of dollars and can develop flaws due to poor preheating in the vulcanizing or recapping operations. A need arises, therefore, for still other means for achieving uniform heating of nonuniform surface products to provide a substantially uniform heating profile.

SUMMARY OF THE INVENTION In accordance with the present invention a microwave heating apparatus is provided with means for maintaining a predetermined distance between an energy applicator and nonuniform article surfaces ay appropriate movement of the energy applicator as controlled by sensing and positioning means. In one embodiment electromechanical actuators and limiters are mounted on a horn-type radiator. Movement of mechanical sensing means such as, for example, a contacting wheel controls the movement of the radiator in a forward and backward direction to establish a substantially uniform heating profile across the entire surface ofa nonuniformly-contoured article. The horn-type radiator is carried by a motorized cart and electrical signals are generated by a wheel contacting the surfaces of the article being heated. in the regions where the surface being heated is beyond the efficient distance, the signals from actuators and limiters provide for the movement of the cart closer to the article. Similarly, where the sensing means indicate a closer than desired spacing of the article surfaces, a reverse switch actuator moves the cart backward to maintain the predetermined spacings.

in another embodiment to be described a movable cart is provided with a sloped track which is directed radially with respect to the axis of rotation of an article being heated. The horn-type radiator is provided with a set of freely rotatable wheels adjacent the open end which contact the surfaces of the rotating article. The movement of the energy radiator towards or away from the surfaces of the article being heated are controlled solely by the forces of gravity.

In all the embodiments a self-contained unit may be provided including the energy source, power supply.

electrical and safety controls, as well as waveguide transmission means, for the distribution of the energy terminating in a horn-type radiator. The means for supporting articles to be heated within an enclosure radiated with microwave energy, may include a horizontally rotatable turntable. In addition it is possible to have the article rotated vertically. Further, electronic, as well as mechanical, means for the sensing of the article surfaces during the processingmay be employed.

BRIEF DESCRIPTION OF THE DRAWINGS Details of the illustrative embodiments of the invention will now be described with reference being directed to the accompanying drawings, wherein:

FIG. 1 is a side elevational view of an illustrative embodiment of the invention with the article being heated mounted on a horizontally rotatable member;

FIG. 2 is an enlarged plan view of a portion of the sensing and control means for the apparatus in FIG. 1.

FIG. 3 is a side elevational view of an alternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 the illustrative embodiment comprises a plurality of parallel conductive walls 12 which define an enclosure 14. In embodiments for the processing of large diameter pneumatic tires an access opening 16 is provided in a top wall to facilitate the introduction of the article to be heated within the enclosure. A hinged door 18 with means for the prevention of the escape of the electromagnetic energy encloses the opening 16. In the applications involving the large enclosures the entire apparatus is supported on a foundation 20.

Thearticle support means comprise a turntable 22 actuated by a shaft 24 and actuation means coupled to gear 26 to provide for rotation of the turntable, as well as vertical displacement through lead screw 28 anchored to the foundation by plate member 30. The article to be heated such as an annular-shaped pneumatic tire 32 is supported on the turntable 22. It will be notedthat section 36 is substantially thicker than the center of the tread 34. With suitable gearing mechanism such as that described in the aforementioned U.S. Pat. No. 3,745,291 the article to be heated is continuously rotated in the direction indicated by the arrow 38 as well as being vertically displaced as indicated by the arrow 40. The movement of the article support means is programmed at a rate of movement which, illustratively, for the large size pneumatic tires provides rotation speeds at approximately 4 RPM. While the tire casing is rotated the vertical displacement is provided with longer periods of time devoted in the shoulder sections 36 of the tread to achieve temperatures of approximately 200 F. The center section does not require as long a dwell time for the application of the energy. Numerous differential gear mechanisms are also disclosed in the referenced patent for the displacement of the article being heated angularly during rotation, as well as vertically. These gear mechanisms have not been further described in this specification for the sake of clarity since they have been fully disclosed in the referenced patent or are well known in the art.

The electromagnetic energy at a frequency of either 915 or 2450 MHz is provided from a source such as a magnetron 42 coupled to waveguide transmission means 44 of the rectangular type which can include isolators where desired. The waveguide transmission means are terminated in an energy applicator such as a flared openmouthed horn radiator 46. The entire energy applicator apparatus is transported on a motorized cart 48 carried by means of wheels 50 on a set of rails 52 terminating in a bumper structure 54. The conventional high voltage power supplies, as well as all electrical and safety controls are provided within the cart 48. Cables 56 and 58 of the conventional type provide for the coupling of the high voltage supply and control of the magnetron 42. The energy applicator sensing and control means 60 of the invention are secured by brackets 62 to the horn radiator and waveguide means. Referring next to FIG. 2 the details of the sensing and control means 60 will now be described. Mechanical sensor means 64 such as a wheel is carried. by an axle 66 and shaft 68. Spring 70 holds the wheel 64 extended to contact the article surfaces and rests against the ball bushing member 72. Bushing 72 is anchored by bracket 74 to bar member 76. A channel 78 in bar member 76 provides means for the tab 80 of shaft collar 82 attached to shaft 68 to ride and hold wheel 64 in a horizontal plane. Shaft 68 oscillates in a forward and backward direction between bushing 74 and a rear bushing member 84 secured by bracket 86 to base member 88 on which bar member 76 is positioned.

Means for controlling the forward and reverse movement of the horn radiator 46 by movement of the motorized cart 48 is provided by a forward switch actuator 90 and reverse switch actuator 92 spaced along the rod 68. Switches 96 are provided on either side of the shaft with one controlling forward and the other reverse movement when plungers 98 are contacted by actuators 90 or 92. Actuator 90 stops forward motion when the desired position is reached. Actuator 92 starts the motor to reverse the position of cart 48 and the transported radiator 46. As a safety measure an overtravel switch 100 with plunger 102 is provided which automatically terminates the operation of all the electrical means should shaft .68 extend beyond the other switches without producing the desired motion. The distance between the actuators 90 and 92 determines the dwell or dead band when the position of the horn radiator relative to the article being heated remains fixed. When the article having a nonuniform surface causes a change in the sensor wheel position the shaft is moved to reposition the radiator.

Alternative apparatus embodying the invention is illustrated in FIG. 3. The article to be heated, illustratively, a large diameter pneumatic tire casing is supported on a dolly 112 having wheels 114. The tire casing is rotated in the direction indicated by arrow 116 with the path of rotation vertical and controlled by the turntable 118 supported on axle 120. The gearing and actuating mechanism has again been omitted for the sake of clarity.

The sensing and energy applicator positioning means comprise a movable cart 122 having on its upper surface a sloped track with rails 124 which extends radially with respect to the axis of the rotation. Another movable cart 126 having wheels 128 rides on the sloped track 124 and supports energy applicator 130 including the microwave energy source 132, waveguide transmission line 134, including an isolator 136, and a flared open-mouthed horn-type radiator 138. The end of radiator 138 adjacent to the article to be heated is provided with a plurality of freely rotatable wheels 140 which are adapted to ride on the outer surfaces of the tire casing 110. The position of the surfaces of the article being heated with relation to the horn-radiator 138 is controlled in this embodiment by the forces of gravity so that in the outermost position the cart 126 is disposed near the top of track 124. Movement of the tire casing to the shoulder region 142 results in the movement of the cart 126 and the supported horn radiator closer to the surface being heated. In this embodiment the desired predetermined distance between the surface to be heated and the radiator is determined by adjustments of the distance between wheels 140 and the mouth of the radiator. The movable cart 122 and dolly 112 during the processing operation may be maintained stationary by means of blocks 144 and 146.

A unique structure is, therefore, disclosed for automatically compensating for the variations in the surfaces being heated with relation to the microwave energy applicator throughout the processing operation. The invention is particularly useful where articles of nonuniform cross-sectional contours are involved and a desired heating profile must be maintained throughout the article. Numerous modifications, variations and alterations will be evident to those skilled in the art. The foregoing description of the illustrative embodiments is, therefore, intended to be interpreted broadly rather than in a limiting sense.

What is claimed is: 1. Microwave heating apparatus comprising: an enclosure; an electromagnetic energy source; means for supporting and rotating an article having a substantially nonuniform cross-sectional contour to be heated within said enclosure; means for radiating said article with said energy comprising waveguide feed means coupled to said source and terminating in a horn energy radiator with said waveguide and source mounted on a vehicle adapted to be moved relative to said rotating article; and means for controlling the positioning of said radiator relative to the exterior surfaces of the rotating article comprising a freely rotatable wheel in continuous contact with said rotating article when said energy is radiated secured adjacent to the end of said radiator and means for moving said vehicle relative to said rotating article actuated by the substantially horizontal linear movement of said wheel. 2. The apparatus according to claim 1 wherein said vehicle is supported on a sloped track carried by a second vehicle with said second vehicle being maintained stationary while said article is rotating. 

1. Microwave heating apparatus comprising: an enclosure; an electromagnetic energy source; means for supporting and rotating an article having a substantially nonuniform cross-sectional contour to be heated within said enclosure; means for radiating said article with said energy comprising waveguide feed means coupled to said source and terminating in a horn energy radiator with said waveguide and source mounted on a vehicle adapted to be moved relative to said rotating article; and means for controlling the positioning of said radiator relative to the exterior surfaces of the rotating article comprising a freely rotatable wheel in continuous contact with said rotating article when said energy is radiated secured adjacent to the end of said radiator and means for moving said vehicle relative to said rotating article actuated by the substantially horizontal linear movement of said wheel.
 2. The apparatus according to claim 1 wherein said vehicle is supported on a sloped track carried by a second vehicle with said second vehicle being maintained stationary while said article is rotating. 